Plenum cables are generally used in buildings where fire codes require flame retardant cables. Typically plenum data cables have two or more pairs of insulated conductors in a common jacket. The insulation can be made of several types of flame retardant insulation. A typical and widely used flame retardant insulation for conductors in data plenum cables is fluorinated ethylene-propylene (FEP Teflon.RTM.). FEP Teflon.RTM. insulation is presently in short supply and is somewhat difficult to extrude. Thus, special extrusion equipment is needed to extrude FEP Teflon.RTM..
Due to problems with phase delay, skew and smoke and flame properties, all of the insulated conductors in the plenum cable have the same insulation.
The present invention is directed to providing a plenum cable which has other than FEP on at least one insulated conductor and therefore displaces the fluorinated ethylene-propylene on one or more plenum data cable insulated conductors and reduce the need for fluorinated ethylene-propylene insulation.
The present invention also provides a plenum cable having more than one insulated conductor surrounded by a jacket. At least one of the insulator conductors has a different insulator than another insulated conductor and all of the insulated conductors have substantially the same dielectric constant.